Long term: try to track where each email is used in critical services for communication purposes (banks, financial apps, government services)
Short term: go through your email dumps and create filters for common spammers. Unsubscribe if possible.
Create filters by common marketing patterns. Examples: too much punctuation, too many emojis, too many images, too many links, some marketing keywords like “hurry”, “offer”, “saving”
Create rules for categorizing the emails. Like Login Security/Account info, Statements, Bills/Receipts, promotions (that come from a important site), etc.
My stepwise plan: